The present invention is in the field of imaging systems. More particularly, the present invention provides a thin-wall drum for an external drum imaging system.
In external drum imaging systems, a movable optical carriage is commonly used to displace an image recording source in a slow scan direction while a cylindrical drum, having recording media mounted on an external surface thereof, is rotated with respect to the image recording source. The drum rotation causes the recording media to advance past the image recording source along a fast scan direction that is substantially perpendicular to the slow scan direction.
The image recording source may include an optical system for generating one or more imaging beams that are scanned across the surface of the recording media. Each imaging beam may be separately modulated according to a digital information signal representing data corresponding to the image to be recorded.
The recording media to be imaged by an external drum imaging system is commonly supplied in discrete, flexible sheets, hereinafter collectively referred to as xe2x80x9cprinting plates.xe2x80x9d Each printing plate may comprise one or more layers supported by a support substrate, which for many printing plates is a plano-graphic aluminum sheet. Other layers may include one or more image recording (i.e., xe2x80x9cimageablexe2x80x9d) layers such as a photosensitive, radiation sensitive, or thermally sensitive layer, or other chemically or physically alterable layers. Printing plates that are supported by a polyester support substrate are also known and can be used in the present invention. Printing plates are available in a wide variety of sizes, typically ranging, e.g., from 9xe2x80x3xc3x9712xe2x80x3, or smaller, to 58xe2x80x3xc3x9780xe2x80x3, or larger.
A cassette is often used to supply a plurality of unexposed printing plates to an external drum imaging system. The printing plates are normally supplied in stacks of ten to one hundred, depending upon plate thickness, and are stored in the cassette. A plate manager may be used to automatically and selectively unload and feed a printing plate from a plurality of different cassettes to the external drum imaging system for imaging.
The throughput of an external drum imaging system (e.g., the number of plates/hour that can be imaged by the system) is dependent upon a multitude of factors. For example, the time required for a stationary external drum to be rotated up to the speed required for imaging (e.g., 100-1000 revolutions per minute (rpm)), or conversely, the time required to bring a rotating external drum to a stop to remove imaged recording media and then load new recording media, greatly affects the throughput of the imaging system.
The throughput of the imaging system may be increased, therefore, by increasing the rotational (angular) acceleration/deceleration of the external drum. This may be achieved, for example, by using larger and more powerful drive motors, power supplies, braking systems, etc. Unfortunately, this tends to greatly increase the complexity, cost, size, etc., of the imaging system. Alternately, or in addition, the weight of the drum itself can be reduced. One example of a light-weight external drum for an imaging system is disclosed in U.S. Pat. No. 6,250,221, incorporated herein by reference. The external drum in this patent is formed from aluminum using an extrusion process. Although lighter than previously available external drums, this drum is fairly expensive to manufacture.
There is a need, therefore, for a drum that is both light-weight and less-expensive to produce, and which can be used for the high resolution imaging of printing plates in an external drum imaging system.
The present invention provides a thin-wall drum for an external drum imaging system.
Generally, the present invention provides an apparatus comprising an external drum for supporting a printing plate to be imaged by an imaging system, wherein the external drum has a wall thickness less than or equal to about 1.5 percent of an outside diameter of the external drum.
The present invention also provides an external drum platesetter comprising an external drum having a media support surface and a scanning system for imaging data onto a printing plate mounted on the media support surface of the external drum, wherein the external drum has a wall thickness less than or equal to about 1.5 percent of an outside diameter of the external drum.